Definitely Archetto/Hildergard, she was an absolute nobody in my mind for years, then The Masses' Travels gave her one of the most poignant exchanges in the franchise after putting in perspective that someone that has lived her life in earnest with all the ups and downs can ultimately be reduced to Meaningless And Worthless in a culture based on Magical Phrenology. I really like the moments of vulnerability and sincerity that Arknights tends to be able to portray, especially contrasted with the bigger than life moments I think a lot of people tend to remember as iconic instead, especially when it's payoff for listening and getting immersed. Hildergard could've easily reacted by going John Wick or something, but the raw drowning pain she expresses and then subsequently processes adequately is worth its weight in gold, far more than "then suddenly popular character saves her and all is fine", I appreciate that it was given the gravitas of someone's life work being basically swept aside literally for racism in the ethnostate that suddenly said the quiet part loudly.